Mounting mat for fragile structures such as catalytic converters

ABSTRACT

A device for the treatment of exhaust gases such as a catalytic converter, a diesel particulate trap and the like, includes a housing having an inlet at one end and an outlet at its opposite end through which exhaust gases flow; a structure resiliently mounted within the housing, the structure having an outer surface and an inlet end surface at one end in communication with the inlet of the housing and an outlet end surface at an opposite end in communication with the outlet of the housing; and mounting element, disposed between the structure and the housing, for selectively exerting substantially stable mounting pressure against the housing and the structure over a temperature range of from about 20° C. to at least about 1200° C., wherein the mounting element is a flexible mounting mat including an integral, substantially non-expanding sheet comprising ceramic fibers, wherein the fibers are substantially shot free. The mat has flexible, structural integrity. A method of mounting a fragile structure in a device is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 08/470,995filed on Jun. 6, 1995, now U.S. Pat. No. 5,666,726, which is adivisional application of Ser. No. 08/333,968 filed on Nov. 3, 1994, nowU.S. Pat. No. 5,580,532, which is a continuation-in-part application ofSer. No. 08/051,469 filed Apr. 22, 1993, now abandoned.

FIELD OF THE INVENTION

The present invention is directed to catalytic converters, dieselparticulate traps and other devices for the treatment of exhaust gases.More particularly, the present invention is directed to a device for thetreatment of exhaust gases having a catalyst support structure mountedwithin a housing which is supported therein by a mounting means havingenhanced handleability and fabrication characteristics comprising anintegral, substantially nonexpanding composite mat of ceramic fiber formounting and supporting the support structure.

BACKGROUND OF THE INVENTION

Catalytic converter assemblies for treating exhaust gases of automotiveand diesel engines contain a catalyst support structure for holding thecatalyst, used to effect the oxidation of carbon monoxide andhydrocarbons and the reduction of oxides of nitrogen, the supportstructure being mounted within a metal housing. The support structure isgenerally made of a frangible material, such as a monolithic structureformed of metal or a brittle, fireproof ceramic material such asaluminum oxide, silicon dioxide, magnesium oxide, zirconia, cordierite,silicon carbide and the like. These materials provide a skeleton type ofstructure with a plurality of tiny flow channels. These structures arevery fragile however. In fact, these monolithic structures are sofragile that small shockloads or stresses are often sufficient to crackor crush them.

The support structure is contained within a metal housing, with a spaceor gap between the external surface of the support structure and theinternal surface of the housing. In order to protect the supportstructure from thermal and mechanical shock and other stresses notedabove, as well as to provide thermal insulation, it is known to positionat least one sheet of mounting material within the gap between thesupport structure and the housing. For example, U.S. Pat. Nos.4,863,700, 4,999,168, and 5,032,441, each of which is incorporatedherein by reference, disclose catalytic converter devices having amounting material disposed within the gap between the housing and thesupport structure contained in the devices to protect the fragilesupport structure and otherwise hold it in place within the housing.

However, the conventional mounting materials used in these catalyticconverter devices, while suitable for most current automotive catalyticconverters, exhibit difficulties when the catalytic converter operatingtemperature is either very low (20°-300° C.) or very high (750°-1200° C.and above). For instance, when these conventional mounting materialshave been used in catalytic converters for vehicles having a highergross weight than normal gasoline powered passenger automobiles, theyhave exhibited failure. Because of their high gross vehicle weight, theengines of such vehicles operate at a much higher percentage of theirmaximum output for a much greater percentage of their operating time,than do the engines in passenger automobiles. These operating conditionsin heavier vehicles result in maximum catalytic converter temperaturesof much greater than 850° C. In fact, converter monolith temperatures of1050° C. are not uncommon, and temperatures in excess of 1200° C. may beencountered.

Heretofore, a typical passenger automobile catalytic converter, such asthe one shown in U.S. Pat. No. 5,032,441, utilized a ceramic monolithwhich was supported by an intumescent mounting material having a nominalthickness of about 4.95 mm to about 9.9 mm and a nominal density ofabout 0.63 g/cm³. This material was compressed during installation ofthe ceramic monolith into its metallic housing to a nominal thickness ofabout 3.1 mm to about 6.2 mm and a nominal density of about 1 g/cm³. Theconventional intumescent mounting material contains vermiculite whichexpands at about 300° C. and degrades at temperatures greater than 750°C. Thus, upon the initial heating of the catalytic converter assembly,particularly the initial cycles, conventional intumescent mountingmaterials experience a tremendous expansion pressure which is capable ofcrushing the catalyst support structure and causing component failure.

Accordingly, a need exists for maintaining a constant pressure on themetallic housing and the catalyst support structure under allconditions. In other words, a mounting mat which does not expandsubstantially upon initial heating of the catalytic converter assemblyis seen as highly desirable.

While conventional intumescent mounting material meets the needs of mostcurrent automotive catalytic converters, it does not meet the needs ofseveral near future requirements as well as some current diesel andheavy duty truck requirements. These requirements are focused upon themaintenance of near constant residual mounting pressure in temperatureregimes below 300° C. and above 750° C. Conventional intumescentmounting material cannot provide such a constant pressure at theseextreme temperature regimes.

Examples of severe condition applications in which these properties areimportant include the following: 1) Close-coupled converters which aremounted closer to the engine for better conversion efficiency via highergas temperatures (about 750° C.); 2) Diesel convertors and dieselparticulate traps which operate at low temperatures and which arecommonly pre-heated at 500° C. to pre-expand the intumescent mat priorto installation in the vehicle. This "pre-heating" would be unnecessarywith the mounting mat of the present invention. 3) Heavy-duty truckconverters and motorcycle converters which run at temperatures whichgreatly exceed 750° C. 4) Thin wall monoliths which will assist inmeeting future EPA requirements via reaching operating temperaturequicker due to their lighter mass. These monoliths are weak and will becrushed by the dramatic pressure increase of intumescent mounting mats.

Intumescent mounting mats would fail in the above cited severe conditionapplication examples due to lack of expansion at low temperatures, tohigh pressure excursions between 300°-750° C., and to loss of pressureabove 750° C. With lack of expansion or loss of pressure the fragilemonolith would be released, rattle about within the can, andself-destruct due to mechanical shock. With high pressure excursions,low strength monoliths would be crushed.

Alternative mounting mats, such as those having intumescent sheetmaterial stitch-bonded thereto as described in U.S. Pat. No. 4,929,429,have also been investigated for severe condition applications. However,these mats have been found to be difficult and cumbersome to handle andto fabricate into catalytic converter assemblies. The mounting materialsproposed to accommodate the severe condition applications are themselvesfragile, and require expensive preprocessing such as stitchbinding priorto installation. Moreover, the mounting material used may requirecombination with other mounting materials, such as intumescent sheetsand backing layers, in order to provide sufficient strength forhandleability. These mounting materials are generally very thick andlack structural integrity, even being handled in a bag to preventcrumbling. Thus they are difficult to cut to size for installation, andfurther must be compressed substantially to fit enough material neededfor supportive mounting within the gap between the catalyst supportstructure and the housing. Consequently, "flashing" commonly occurs,with excess material being squeezed out of the housing.

Another alternative mounting mat is shown in U.S. Pat. No. 3,771,967. Nostitchbinding is employed in for the mounting mat of this patent.Instead, this patent discloses that the ceramic fiber layer or ringwhich comprises the mounting mat may be impregnated with a binder and arigidizer to adhere the fibrous mounting material to the metal housingor shell. This mounting mat, hardened with binder and rigidizer, lacksthe flexibility necessary to prevent the support structure from beingcrushed or otherwise damaged during use in the extreme conditions notedhereinabove. Other examples of alternate approaches besides thosedescribed in U.S. Pat. Nos. 4,929,429 and 3,771,967, are found in U.S.Pat. Nos. 4,693,338 and 5,028,397.

Diesel particulate traps similarly include one or more porous tubular orhoneycomb-like structures (having channels closed at one end, however)which are mounted by a thermally resistant material within a housing.Particulate is collected from exhaust gases in the porous structureuntil regenerated by a high temperature burnout procedure, whichthermally taxes the mounting material.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a device for thetreatment of exhaust gases which includes a mounting mat possessing goodhandleability and fabrication characteristics.

It is another object of the present invention to provide a deviceincluding a mounting mat, as above, the mounting mat being capable ofwithstanding high temperatures without degradation while maintainingstable pressure over a wide range of operating temperatures.

It is still another object of the present invention to provide a deviceincluding a substantially nonexpanding mounting mat, as above, whereinthe mounting mat remains flexible and does not require the use ofadditional means to maintain its structural integrity.

The present invention provides a device for treatment of exhaust gasescomprising:

(a) a housing having an inlet at one end and an outlet at its oppositeend through which exhaust gases flow;

(b) a structure resiliently mounted within said housing, said structurehaving an outer surface and an inlet end surface at one end incommunication with said inlet of said housing and an outlet end surf aceat its opposite end in communication with said outlet of said housing;

(c) mounting means, disposed between said structure and said housing,for selectively exerting substantially stable mounting pressure againstsaid housing and said structure over a temperature range of about 20° C.to at least about 1200° C., wherein said mounting means is a flexiblemounting mat in contact with and covering at least a portion of saidouter surface of said structure and includes an integral, substantiallynon-expanding composite sheet of ceramic fibers and a binder, whereinsaid fibers are substantially shot free.

The mounting mat of the present invention may be used to mount anyfragile or frangible structure, such as an automotive catalyticconverter catalyst support monolith or diesel particulate trap, and thelike, in all expected temperature environments where protection fromthermal and mechanical shock is desirable. The mounting mat of thepresent invention maintains a near constant pressure over the entireoperating range of all current and known future converter/trap designs.Throughout this specification, references to catalytic converters shouldbe considered generally to apply to diesel particulate traps.

A method is provided by the present invention of mounting a fragilestructure having at least one inlet face within a device having ahousing to provide thermal insulation and mechanical shock resistancecomprising: wrapping mounting means such as a flexible mounting matcomprising an integral, substantially nonexpanding composite sheet ofceramic fibers and binder around the entire perimeter of at least aportion of the structure's surfaces adjacent to the inlet face, andforming a housing around the wrapped structure and radially compressingthe mounting mat between the structure and the housing, wherein thefibers are substantially shot free and wherein said mounting means isfor exerting substantially stable pressure over an operating temperaturerange of about 20° C. to at least about 1200° C. For use in catalyticconverters or diesel particulate traps, said composite sheet has anuninstalled nominal thickness of about 3 mm to about 30 mm, anuninstalled nominal density of about 0.03 to about 0.3 grams per cubiccentimeter, and an installed thickness of about 2 mm to about 8 mm and agap bulk density of about 0.1 to about 1.5 grams per cubic centimeter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, elevational view of a catalytic converteraccording to the present invention.

FIG. 2 is a graphical representation of pressure versus temperature formounting mats of the present invention compared to conventionalconverter mats at various gap bulk densities.

FIG. 3 is a graphical representation of pressure versus temperature formounting mats of the present invention at various gap bulk densities.

DETAILED DESCRIPTION OF THE INVENTION

One representative form of a device for treating exhaust gases is shownas a catalytic converter, generally designated by the numeral 10 inFIG. 1. It will be understood that the present invention is not intendedto be limited to use in the catalytic converter shown, and so the shapeis shown only as an example to illustrate the invention. In fact, asnoted hereinabove, the mounting mat could be used to mount any fragilestructure, such as a diesel particulate trap or the like. Nonautomotiveapplications for the mounting mat of the present invention include butare not limited to catalytic converters for chemical industry emission(exhaust) stacks. The term fragile structure is intended to mean andinclude structures such as metal or ceramic monoliths or the like whichare fragile or frangible in nature and would benefit from a mounting matsuch as is described herein.

Catalytic converter 10 includes a generally tubular housing 12 formed oftwo pieces of metal, e.g. high temperature-resistant steel. Housing 12includes an inlet 14 at one end and an outlet (not shown) at itsopposite end. The inlet 14 and outlet are suitably formed at their outerends whereby they may be secured to conduits in the exhaust system of aninternal combustion engine. Device 10 contains a fragile catalystsupport structure, such as a frangible ceramic monolith 18 which issupported and restrained within housing 12 by mounting means such as mat20, to be further described. Monolith 18 includes a plurality ofgas-pervious passages which extend axially from its inlet end surface atone end to its outlet end surface at its opposite end. Monolith 18 maybe constructed of any suitable refractory metal or ceramic material inany known manner and configuration. Monoliths are typically oval orround in cross-sectional configuration, but other shapes are possible.

In accordance with the present invention, the monolith is spaced fromits housing by a distance or a gap, which will vary according to thetype and design of converter or trap utilized. This gap is filled withmounting mat 20 to provide resilient support to the ceramic monolith 18.The resilient mounting mat 20 provides both thermal insulation to theexternal environment and mechanical support to the catalyst supportstructure, protecting the fragile structure from mechanical shock. Themounting mat 20 also possesses good handleability and is easilyprocessed in the fabrication of devices utilizing its capabilities ofmaintaining substantially stable pressure under compression in fixed gapconditions over a wide range of operating temperatures.

The mounting mat 20 comprises an integral, substantially non-expandingcomposite sheet of ceramic fibers and a binder. By "integral" is meantthat after manufacture the mounting mat has self supporting structure,needing no reinforcing or containment layers of fabric, plastic orpaper, (including those which are stitch-bonded to the mat) and can behandled or manipulated without disintegration. By "substantiallynon-expanding" is meant that the sheet does not readily expand upon theapplication of heat as would be expected with intumescent paper. Ofcourse, some expansion of the sheet does occur based upon its thermalcoefficient of expansion. The amount of expansion, however, is veryinsubstantial as compared to the expansion which occurs based uponintumescent properties. It will be appreciated that the mounting mat issubstantially devoid of intumescent materials.

Ceramic fibers which are useful in the mounting mat of the presentinvention include polycrystalline oxide ceramic fibers such as mullite,alumina, high alumina aluminosilicates, aluminosilicates, zirconia,titania, chromium oxide and mixtures thereof. The ceramic fibers arepreferably refractory. When the ceramic fiber is an aluminosilicate, thefiber may contain between about 55 to about 98% alumina and betweenabout 2 to about 45% silica, with the preferred ratio of alumina tosilica being between 70 to 30 and 75 to 25. Suitable polycrystallineoxide refractory ceramic fibers and methods for producing the same arecontained in U.S. Pat. Nos. 4,159,205 and 4,277,269, which areincorporated herein by reference. FIBERMAX® polycrystalline mulliteceramic fibers are available from The Carborundum Company, NiagaraFalls, N.Y. in blanket, mat or paper form.

The fibers used in the present invention are also characterized by beingsubstantially shot free, having very low shot content, generally on theorder of about 5 percent nominally or less. The diameters of fibersuseful in the present invention are generally about 1 micron to about 10microns.

The binder used in the present invention is typically an organic binderwhich is preferably sacrificial in nature. By "sacrificial" is meantthat the binder will eventually be burned out of the mounting mat,leaving only the ceramic fibers as the final mounting mat.

Suitable binders include aqueous and nonaqueous binders, but preferablythe binder utilized is a reactive, thermally setting latex which aftercure is a flexible material that can be burned out of the installedmounting mat as indicated above. Examples of suitable binders or resinsinclude, but are not limited to, aqueous based latexes of acrylics,styrene-butadiene, vinylpyridine, acrylonitrile, vinyl chloride,polyurethane and the like. Other resins include low temperature,flexible thermosetting resins such as unsaturated polyesters, epoxyresins and polyvinyl esters. Specific binders useful in the presentinvention include but are not limited to HISTRETCH V-60™, a trademark ofB. F. Goodrich Co. (Akron, Ohio) for acrylonitrile based latex. Solventsfor the binders can include water, or a suitable organic solvent, suchas acetone, for the binder utilized. Solution strength of the binder inthe solvent (if used) can be determined by conventional methods based onthe binder loading desired and the workability of the binder system(viscosity, solids content, etc.).

The mounting mat of the present invention can be prepared byconventional papermaking techniques. Using this process, ceramic fibersare mixed with a binder to form a mixture or slurry. Any mixing meansmay be used, but preferably the fibrous components are mixed at about a0.25% to 5% consistency or solids content (0.25-5 parts solids to99.5-95 parts water). The slurry may then be diluted with water toenhance formation, and it may finally be flocculated with flocculatingagent and drainage retention aid chemicals. Then, the flocculatedmixture or slurry may be placed onto a papermaking machine to be formedinto a ceramic paper mat. The mats or sheets may be formed by vacuumcasting the slurry or mixture with conventional papermaking equipmentand are typically dried in ovens. For a more detailed description of thestandard papermaking techniques employed, see U.S. Pat. No. 3,458,329,the disclosure of which is incorporated herein by reference. This methodtypically breaks the fibers during processing. Accordingly the length ofthe fibers are generally about 0.025 cm to about 2.54 cm when thismethod is used.

Alternatively, the ceramic fibers may be processed into a mat byconventional means such as dry air laying. The mat at this stage, hasvery little structural integrity and is very thick relative to theconventional catalytic converter and diesel trap mounting mats.

Where this alternative technique is used, the mat may be furtherprocessed by the addition of a binder to the mat by impregnation to forma discontinuous fiber composite. In this technique, the binder is addedafter formation of the mat, rather than forming the mat prepreg as notedhereinabove with respect the conventional papermaking technique. Thismethod of preparing the mat aids in maintaining fiber length by reducingbreakage. Generally the length of the fibers are about 1 cm to about 10cm, preferably about 1.25 cm to about 7.75 cm when this method is used.

Methods of impregnation of the mat with the binder include completesubmersion of the mat in a liquid binder system, or alternativelyspraying the mat. In a continuous procedure, a ceramic fiber mat whichcan be transported in roll form, is unwound and moved, such as on aconveyer or scrim, past spray nozzles which apply the binder to the mat.Alternatively, the mat can be gravity-fed past the spray nozzles. Themat/binder prepreg is then passed between press rolls which removeexcess liquid and densify the prepreg to approximately its desiredthickness.

The densified prepreg may then be passed through an oven to remove anyremaining solvent and if necessary to partially cure the binder to forma composite. The drying and curing temperature is primarily dependentupon the binder and solvent (if any) used. The composite can then eitherbe cut or rolled for storage or transportation.

The mounting mat can also be made in a batch mode, by immersing asection of the mat in a liquid binder, removing the prepreg and pressingto remove excess liquid, thereafter drying to form the composite andstoring or cutting to size.

The resin loading level in the composite is generally on the order ofabout 0.5% to about 20%, and preferably is about 2% to about 7%. Thecompressed, bonded composite is flexible and has structural integrityand good handleability.

Regardless of which of the above-described techniques are employed, thecomposite can be cut, such as by die stamping, to form mounting mats ofexact shapes and sizes with reproducible tolerances. The compositemounting mat may be bent back upon itself without cracking, due to itsflexibility. This mounting mat 20 can be easily and flexibly fittedaround the catalyst support structure 18 without cracking and fabricatedinto the catalytic converter housing 12 to form a resilient support forthe catalyst support structure 18, with minimal or no flashing such asby extrusion or flow of excess material into the flange area 16. Thehandleability and processability of the mounting mat 20 will permit thefabrication of the catalytic converter assembly 10 to be substantiallyautomated.

Having describe the invention is general terms, it is now illustrated ingreater detail by way of an example. It will be understood that thisExample is for illustration only and should not be considered limitingin any respect, unless otherwise stated.

EXAMPLE

A mounting mat composite was prepared in a batch mode by placing a 12inch by 36 inch (30 cm by 91 cm) mat of FIBERMAX® polycrystallineceramic fibers on a wax paper covered sheet of plexiglass in a containerand pouring onto the mat a 3% solution of HI STRETCH V60™ acrylonitrilebased latex in water, in an amount calculated to give a loading of 6.5%organics in the composite. An aluminum screen was pressed on top of themat to extract excess binder solution, and was removed. Wax paperfollowed by plexiglass was placed over the mat to form a sandwichorientation, and the assembly was pressed in a Williams paper press to athickness of 3/16 inch (about 0.5 cm). The glass and wax paper wereremoved and the impregnated mat was placed on a mold release-treatedaluminum foil in an oven to dry at 145°-150° C. for 45 to 60 minutes.The dried composite was strong, flexible and easy to handle.

The mounting mat of the present invention generally has a nominalthickness (before compression during device assembly) of about 3 mm toabout 30 mm. The nominal density, being the calculated density of themounting mat without being compressed, is generally about 0.03 to about0.3 grams per cubic centimeter.

When the mounting mat 20 is placed into the catalytic converter 10during fabrication of the device, the mounting mat is radiallycompressed between the members of the housing 12 to a thicknesscorresponding to the gap between the housing 12 and the catalyst supportstructure 18, generally about 2 mm to about 8 mm, preferably about 2 mmto about 6 mm. This increases the density of the mounting mat, to itsfinal gap bulk density, and results in the mounting mat exertingpressure under operating conditions against the adjacent elements 12 and18. Depending upon the application, the mounting mats of the presentinvention can exert stable mounting pressures from about 0.1 Kg/cm² toabout 50 kg/cm².

In operation, the catalytic converter experiences a significant changein temperature. Due to the differences in their thermal expansioncoefficients, the housing 12 may expand more than the support structure18, such that the gap between these elements will increase slightly. Thethickness of mounting mat 20 is selected such that even at operatingtemperatures the gap is filled with mounting mat material, although at aslightly lower pressure than at ambient temperatures, to prevent thesupport structure 18 from vibrating loose. The substantially stablemounting pressure exerted by the mounting mat 20 under these conditionspermits accommodation of the thermal characteristics of the assemblywithout compromising the physical integrity of the constituent elements.

Conventional intumescent mats may experience an increase of pressure ofup to 800% upon heating to operating temperatures under standard testfixed gap conditions. Even in expanding gap conditions of normaloperation, these conventional mats may crack fragile catalyst supportstructures. The mounting mat of the present invention maintainssubstantially stable mounting pressure under standard test fixed gapconditions, and may experience a slight decrease in pressure of up toabout 30% in strenuous operating, expanding gap conditions at a givenbulk density. The selection of bulk density for mounting mat 20 in agiven application will maintain the necessary protective mountingpressure on the housing 12 and support structure 18.

Fixed gap pressure measurements are carried out in an enclosed furnacechamber having a roof orifice and a floor orifice. A pair of fusedquartz rams are placed in the furnace, one per orifice. The quartz ramsare of sufficient length to extend from the furnace's center to adistance beyond the furnace's exterior shell. At the center of thefurnace the two quartz ram ends form the "fixed gap" between which thesample is placed. Outside the furnace the extending rams are rigidlymounted to load cells. The sample's pressure characteristics, in aspecified fixed gap condition, are monitored by these load cells as thefurnace is ramped upwards in temperature.

FIG. 2 is a graph showing pressure of mounting mats according to thepresent invention as compared to intumescent papers at various gap bulkdensities under fixed gap conditions. It is demonstrated that in theinventive device, the mounting mat will exert a stable, substantiallyconstant mounting pressure over a wide temperature range as compared toconventional intumescent papers.

FIG. 3 is a graph showing pressure of mounting mats to be used in adevice according to the present invention over a range of temperaturesunder fixed gap conditions. Again, stable, substantially constantmounting pressure throughout the temperature range is demonstrated.

Unlike intumescent materials, such as vermiculite, the holding force onthe support structure in the inventive device is generated by theresilient fibers in the mat, not the expansion of vermiculite. Thedramatic expansion pressure increase during the initial thermal cyclesobserved using conventional catalytic converter mounting materials arenot observed using a mounting mat according to the present invention. Infact, the mounting mat according to the invention will function untilthe limit of the fibers is reached, at approximately 1650° C. foraluminosilicate ceramic fibers.

A mounting mat according to the present invention was prepared fromFIBERMAX® polycrystalline ceramic fibers and tested for hot gas erosionresistance using the traditional procedure used to measure conventionalconverter mats. The test conditions were maintaining an oven temperatureof 600° C. while pulsing air 2.0 seconds on and 0.5 seconds off, at anair velocity of 300 meters per second. Conventional intumescent papermats eroded 2.54 cm in 2 to 82 hours, while the mounting mat of thepresent invention showed no erosion in 100 hours of testing.

The superior physical property characteristics demonstrated by themounting mats of the present invention over conventionalconverter/diesel trap mats, such as high erosion resistance andsubstantially constant, stable pressure over a wide temperature range,are desirable in both catalytic converter and diesel trap designs. Themounting mats can be die cut and are additionally operable as resilientsupports in a thin profile, providing ease of handling, and in aflexible form, so as to be able to provide a total wrap of the catalystsupport structure without cracking. Alternatively, the mounting mat maybe integrally wrapped about the entire circumference or perimeter of atleast a portion of the catalyst support structure. The mounting mat mayeliminate the need for an end-seal currently used in conventionalconverter devices to prevent gas by-pass.

The mounting mat of the present invention is useful in applications suchas catalytic converters or diesel particulate traps which utilize lowstrength monoliths and/or experience either unconventionally lowoperating temperatures (less than about 300° C.) or high operatingtemperatures (above about 750° C.), as well as traditional mounting matapplications which currently use difficult to handle containment/fiberblanket forms.

The mounting mat of the present invention can also be used in catalyticconverters employed the chemical industry which are located withinexhaust or emission stacks, and which also contain fragile honeycombtype structures to be protectively mounted.

Thus, the objects of the invention are accomplished by the presentinvention, which is not limited to the specific embodiments describedabove, but which includes variations, modifications and equivalentembodiments defined by the following claims.

We claim:
 1. A diesel particulate trap for the treatment of exhaustgases comprising:(a) a housing through which exhaust gases flow; (b) aporous structure for collecting particulate from the exhaust gases,resiliently mounted within said housing; (c) mounting means, disposedbetween said structure and said housing, for selectively exertingsubstantially stable mounting pressure against said housing and saidstructure over a temperature range of from about 20° C. to at leastabout 1200° C., wherein said mounting means is a flexible mounting matin contact with and covering at least a portion of an outer surface ofsaid structure and includes an integral, substantially non-expandingsheet of ceramic fibers, wherein said fibers are substantially shotfree.
 2. The diesel particulate trap as in claim 1 wherein said flexiblemounting mat is integrally wrapped about an entire perimeter of at leasta portion of said structure.
 3. The diesel particulate trap as in claim1 wherein said fibers are selected from the group consisting of alumina,mullite, high alumina aluminosilicates, aluminosilicates, zirconia,titania, chromium oxide and mixtures thereof.
 4. The diesel particulatetrap as in claim 3 wherein said fibers are aluminosilicate comprisingabout 55% to about 98% alumina and about 2% to about 45% silica.
 5. Thediesel particulate trap as in claim 3 wherein said fibers are mullite.6. The diesel particulate trap as in claim 1 wherein said mounting matis compressed to an installed thickness of about 2 mm to about 8 mm. 7.The diesel particulate trap of claim 1 wherein said mounting means isconstructed and arranged to exert a pressure of between about 0.1 kg/cm²and about 50 kg/cm² against said housing and said structure.
 8. Thediesel particulate trap as in claim 1 wherein said sheet has a nominalthickness of about 3 mm to about 30 mm, and a nominal density of about0.03 to about 0.3 grams per cubic centimeter.
 9. The diesel particulatetrap as in claim 1 wherein said ceramic fibers have diameters in therange of about 1 micron to about 10 microns.
 10. The diesel particulatetrap as in claim 1 wherein said ceramic fibers have less than about 5%shot.
 11. The diesel particulate trap as in claim 1 wherein saidmounting mat further includes a sacrificial binder selected from thegroup consisting of latexes of acrylics, styrene-butadiene,vinylpyridine, acrylonitrile, vinyl chloride and polyurethane.
 12. Thediesel particulate trap as in claim 1 wherein said mounting mat includesa sacrificial, flexible thermosetting resin binder selected from thegroup consisting of unsaturated polyesters, epoxies and polyvinylesters.
 13. The diesel particulate trap as in claim 1 wherein saidfibers have an average length in the range of about 0.025 cm to about2.54 cm.
 14. The diesel particulate trap as in claim 1 wherein saidfibers have an average length in the range of about 1 cm to about 10 cm.